The present invention relates to Electronic/Photonic Integrated Circuits, in which optical emitters are integrated with complex integrated circuitry.
Background: Integration of Emissive Electro-Optics
Vast advances have been made in integrated circuit electronics over the last few decades. At the same time, the technology of solid-state lasers has advanced greatly, and such lasers have proven useful in many applications. However, there has been no successful merger of these technologies, and the two have continued to develop along generally separate paths.
Imagers are inherently much simpler to integrate than emissive optics. (Indeed, in the last few years CMOS imagers, which use basically mainstream CMOS technology, have largely displaced even CCD imagers.) Many chips and hybrids have combined an imaging array with drivers or other associated circuitry.
Emissive optics, however, have been much more intractable to integration. Various attempts have been made to propose a technology which would combine emissive optics with complex integrated electronics, but no such proposal has come remotely close to practicability.
Thus while there is a great need for a fully integrated emissive Electro-Photonic Integrated Circuit (“EmEO”) technology, there has been no adequate solution to this need.
Background: GSE Lasers
The Grating-Outcoupled Surface-Emitting (GSE) laser (described in U.S. patent application Ser. Nos. 09/844,484 and 09/845,029, both of which are hereby incorporated by reference), is an essentially planar structure which provides out-of-plane optical emission. The GSE laser has a built in horizontal waveguide that allows on-wafer or on-chip routing and control of light along with emission from the surface of the wafer or chip. In contrast, the light from vertical cavity surface-emitting lasers (VCSELs) is directed normal to the wafer or chip surface and cannot easily be routed within the wafer or chip. The epitaxial structure of a VCSEL is very thick and therefore costly and time consuming to grow, compared to the relatively thin layers making up an edge-emitting (EE) or GSE laser. While EE lasers have a horizontal waveguide and can route light within a wafer or chip, at least one terminating edge (cleaved or etched) is required to access or connect the on-chip light to the outside world. Thus EE lasers are inherently edge-bound (and hence not fully integrable), while VCSELs have incompatibility due to their very special epitaxy requirements.
Integrated Grating-Outcoupled Surface-Emitting Lasers
The present inventors have realized that GSE laser technology provides the foundations for an economical and fully integrable emitter structure, and for a new Emissive Electro-Optic Integrated Circuit technology in which optical emitters (and possibly other optical components) are integrated with complex integrated circuitry. This provides a technology in which on-chip photonic signal channels are combined with unconstrained location of photonic output or input couplers to the outside world. Preferably distributed reflectors are used to define the on-chip laser cavities, so that the locations of laser cavities are not tied to wafer edge or facet locations.
It is highly preferred, in many embodiments, that the optical gain volume (of the emissive photonic elements) and the conductivity-modulation volume (of the active electronic elements) should be formed using a SINGLE body of semiconductor material. Many approaches have been proposed for hybrid structures and for modules, but all have proven to present substantial technological difficulties.
The disclosed innovations, in various embodiments, provide one or more of at least the following advantages:                capability for on-chip routing of optical signals;        combined capability for both on-chip routing and third-dimensional outcoupling of optical signals;        the manufacturing difficulties of faceted wafers are avoided; and        the expensive epitaxy of vertical-cavity lasers is avoided.        